a) Field of the Invention
The invention is directed to a transport container for wafer-shaped objects in which a container enclosure is made up of two lateral regions which are located opposite one another and have projections forming shelves for receiving objects, a base region, a cover region, and a rear wall region, wherein an opening for removing and charging which is located opposite the rear wall region can be closed by a container door and removal and charging are effected in a plane parallel to the surface of the objects.
b) Description of the Related Art
For the purpose of transporting in the production process and for charging semiconductor processing installations, it is known to use so-called SMIF boxes having a relatively small enclosed volume as magazine containers. As is conventional, the box can be placed on an opening mechanism in an enclosure or housing which encloses one or more work stations so as to keep them free of dust. The box and opening mechanism have closing elements which are adapted to one another and which can be opened simultaneously one above the other so that dust particles resting on the outside of the closing elements can be enclosed therebetween when the semiconductor magazine is lowered into the housing together with the two closing elements. The box itself encloses the opening formed in the housing. As a result of cyclical removing and charging movements performed with the opening and closing of the boxes, the particle concentration generated by friction increases on the surfaces of the semiconductors and in the surrounding air.
In order to prevent disruptions in the gas atmosphere in the housing when opening the SMIF box, U.S. Pat. No. 5,169,272 describes a process and a device which provide a stepwise lowering of the releasable bottom accompanied by generation of pressure differentials for the purpose of cleaning the SMIF box. The generated pressure differential prevents gas from entering the clean room during the lowering process or while cleaning the SMIF box with gas which is guided in the region of the bottom from one side of the SMIF box to the opposite side.
In order to ensure the clean room conditions within the box, it is known from EP 313 693 A1 to provide a duct which connects the interior of the SMIF box directly with an exterior region. A vacuum or overpressure can be generated in the SMIF box via the duct and gas can also be transported into the interior. Particles are to be removed by alternately generating pressure and pumping out via a filter located in the interior of the box.
A disadvantage in these solutions consists in that the flow of gas through the interior of the box is incomplete.
An exchange of gas in the SMIF box can be carried out within an effective time period by means of a technical solution according to WO 95/05 002 A1, in which a gas feed duct opens into gas distributing means from closable ducts incorporated in the wall of the box. A gas discharge line communicates with a gas outlet which adjoins the magazine in the opposite direction to that of the gas distributing means.
The technique of SMIF boxes is especially suitable for semiconductor wafers having a conventional small diameter of 100 to 200 mm. In view of the material characteristics of the semiconductor wafers, these SMIF boxes and the magazines used with them are becoming less suitable as transporting containers as the diameters of semiconductor wafers increase.
It is known to use transporting containers constructed according to a completely different design which simultaneously perform the function of magazines. Removal and charging of the semiconductor wafers which are inserted in shelves within the container is effected individually in a plane parallel to the surface of the semiconductor wafers, wherein the transporting container can be closed by a container cover which is directed substantially at right angles to the removal and charging plane. Accordingly, in contrast to the SMIF box, the container cover is removed and inserted laterally rather than in a downward direction. For effective use in semiconductor production, there must be optional access to a plurality of transport container which are stacked one on top of the other.
There is increased technical interest in maintaining the cleanness of the interior of the container since stricter requirements for classes of clean rooms have necessarily resulted due to the fact that the surface of semiconductor wafers has more than doubled and since the absolute quantity of particles increases statistically in the enlarged air volume. Further, a vacuum pressure is instantly generated in the interior when the door of the container is opened resulting in uncontrolled air turbulence so that particles can enter the container and be deposited therein.
Known battery-operated activated boxes which are continuously provided with pure air via an internal filter system have the disadvantage that the required air flow of approximately 0.5 m/s and the output of battery-operated motors associated therewith can no longer be applied as containers become larger, especially if the containers are still to be handled manually.